The present invention relates to a radiation curable coatable composition suitable for use as a floor finish, to a floor finishing system utilizing the composition, to a method for applying a protective coating to a substrate, to substrates coated with the compositions and to a polyfunctional isocyanurate monomer useful in the formulation of the radiation curable coatable compositions.
Polymer compositions are used in the formulation of various coating compositions such as floor finishes, for example. Commercially available floor finish compositions typically are aqueous emulsion based polymer compositions comprising one or more organic solvents, plasticizers, coating aids, antifoaming agents, polymer emulsions, waxes and the like. These compositions typically comprise a relatively low solids content (e.g., about 15-35%). The polymer composition is applied to a floor surface and then allowed to dry in air, normally at ambient temperature and humidity to form a film that serves as a protective barrier against soil deposited on the floor by pedestrian traffic, for example.
Although many of the commercially available floor finishes have performed well and have experienced at least some commercial success, the available finishes have been less than completely satisfactory for several reasons. For example, when applying conventional floor finish compositions to the surface of a floor, several coating applications are typically required to obtain a finish with a suitable appearance. Each successive-application of the composition must be dried before additional coatings are applied and/or before pedestrian traffic is allowed across the treated floor. The compositions are normally dried at ambient temperature and humidity in air, so that the drying time depends upon the air flow over the floor as well as the relative humidity of the air. Conventional floor finishes will soften when exposed to water for short periods or when exposed to strong chemical cleaners during a scrubbing operation, for example. Moreover, such finishes require almost daily maintenance (e.g., buffing) to provide a sustained and desirable appearance.
In light of the foregoing, it is desirable to provide a floor finish composition that can be applied in a single application and immediately dried and hardened in air to provide a durable, low maintenance, water-resistant, chemically resistant finish that does not require labor intensive (e.g., daily) maintenance to provide a sustained and desirable appearance. It would also be desirable to provide such a durable, low maintenance, water-resistant, chemically resistant finish in a form that can readily be removed from the surface to which it is applied, such as from flooring comprising conventional vinyl floor tiles, for example.
It is known that irradiation of ethylenically unsaturated compounds in the presence of a photoinitiator induces photopolymerization. As used herein, xe2x80x9cphotoinitiatorxe2x80x9d refers to any substance or combination of substances that interact with light to generate free radicals capable of inducing free radical polymerization. Photochemical or photoinitiated free radical polymerizations occur when radicals are produced by ultraviolet (xe2x80x9cUVxe2x80x9d) and/or visible light irradiation of a free radical polymerizable reaction system. Energy absorption by one or more compounds in the system results in the formation of excited species, followed by either subsequent decomposition of the excited species into radicals or interaction of the excited species with a second compound to form radicals derived from both the initially excited compound and from the second compound. The exact mechanism for photoinitiation is not always clear and may involve either or both of the aforementioned pathways.
Photochemical polymerization has been applied in the formation of decorative and/or protective coatings and inks for metal, paper, wood and plastics as well as in photolithography for producing integrated and printed circuits and in curing dental materials. Many of the known applications involve a combination of photopolymerization and crosslinking with the crosslinking typically achieved by the used of ethylenically polyunsaturated monomers. Acrylate based systems are common as well as those based on unsaturated polyester and styrene.
Additionally, UV curable protective finishes have been applied to vinyl xe2x80x9cno waxxe2x80x9d flooring during the sheet manufacturing process to provide gloss as well as abrasion resistance. These protective finishes generally cannot be easily stripped from the flooring to which they are applied using conventional stripping methods (e.g., by the application of a chemical stripping composition with a stripping pad or brush). Furthermore, the curing of these finishes is typically carried out using high intensity light. The lamps have high power requirements, large power supplies and generally require ducted venting to remove ozone. Often, these finishes are cured in an inert atmosphere to overcome the deleterious effects of oxygen on the curing process. Because of the above noted power requirements and the like, the use of UV curable polymeric systems in the treatment of flooring has generally been limited to factory scale processes where the expense and additional burdens associated with these systems is more easily justified.
Other problems have been noted in the formulation of UV curable systems for pre-existing flooring (e.g., previously installed in a building). In the application of any type of finish to an existing floor, it is generally preferred that the hardened floor finish not alter the color of the floor. To accomplish this goal, the finish should be transparent and substantially free of observable color. This goal is especially desired in the maintenance of floors composed of white floor tiles where an observable color in the hardened finish will more noticeably produce an observable discoloration in the floor. Additionally, to make a floor finish composition acceptable for application in the field, the applied floor finish should also have low odor prior to curing.
It is known, for example, that certain resins containing functional polymerizable vinyl groups, such as acrylate or vinyl ether/maleate containing an amine or a thiol, are polymerizable in air by free radical polymerization when exposed to UV or visible light in the presence of a photoinitiator. Although tough, abrasion resistant coatings can be provided using such resins, the resulting coatings are typically colored, with colors ranging from yellow to dark orange or have an objectionable odor prior to curing. Consequently, these resins are considered unsuitable for use as floor finishes.
As mentioned, atmospheric oxygen is known to inhibit photoinitiated polymerization reactions, resulting in little or no cure on the surface of the coating or providing a coating with poor surface properties. Various processing techniques have been proposed to eliminate the effects of oxygen from the reacting resin. One approach is to isolate the coating in a chamber and purge the chamber with an inert gas (e.g., nitrogen) so that the polymerization reaction proceeds in an environment substantially free of oxygen. Another approach is to initiate the polymerization reaction using intense UV radiation in conjunction with the high levels of photoinitiator in the uncured resin. Neither of these proposed techniques are practical in providing a floor finish system for use on previously installed flooring. Although smaller, lightweight, inexpensive, low intensity light sources capable of operating on batteries or on 110 volt, 15 amp circuitry would be preferred, known UV curable polymer systems have experienced slower rates of cure and higher cure inhibition when low intensity light has been used.
A long felt and unsolved need exists for a coatable composition suitable for use as a floor finish that can easily be applied to a substrate, such as a previously installed floor, and hardened in air upon exposure to low intensity radiation such as ultraviolet light, for example. It is desirable to provide such a coatable composition, preferably without objectionable odor, in a form that may be easily applied to a floor and subsequently hardened to provide a protective coating substantially free of observable color. It is also desirable to provide the foregoing protective coatings in a form that allows them to be removed from the floor (e.g., by a suitable chemical stripper), as desired.
The invention provides a coatable composition that can be cured quickly in air by exposure to low intensity ultraviolet radiation to provide a durable protective coating for a suitable substrate such as vinyl floor tile, for example. The resulting coating requires little maintenance and can be easily and quickly stripped from the substrate by application of a suitable stripper composition, all as set forth herein.
In one aspect, the invention provides a monomer useful in the formulation of radiation curable coatable compositions, comprising (a) polyfunctional isocyanurate having at least three terminal reactive groups reacted with (b) hydroxyalkyl acrylate and (c) tertiary amine alcohol in a molar ratio of a:b:c of about 1:1-2.5:0.5-2, wherein b+c is at least 3 and no greater than the total number of terminal reactive groups of (a).
A preferred monomer comprises a compound having the general formula: 
wherein
R1 and R2 are H or CH3;
R3 and R4 may independently be alkyl groups (straight, branched or cyclic) having from 1 to 12 carbon atoms, or R3 and R4 may together form a divalent cylcoalkanediyl, oxacycloalkanediyl, or azacycloalkanediyl bridging group having from 2 to 12 carbon atoms; and
Z1, Z2, Z3, Z4, Z5, and Z6 independently represent divalent groups having from 1 to 18 carbon atoms, preferably alkanediyl groups (straight, branched or cyclic) having from 1 to 18 carbon atoms, most preferably, straight chain alkanediyl groups having from 1 to 4 carbon atoms.
The foregoing monomer is formulated into radiation curable coatable compositions as a first monomer by combining it with a second monomer and photoinitiator. The first monomer preferably comprises the reaction product of a trimer of hexane diisocyanate (optionally mixed with an allophanate of hexane diisocyanate), a hydroxyalkyl acrylate, and a tertiary amine alcohol. The first monomer is typically present within the composition in an amount between about 10 and 80 wt %. The second monomer can be selected from any of a variety of polymerizable monomers. Preferably, the second monomer is an acrylate, as is further described herein. The second monomer is typically present within the composition in an amount between about 5 and 90 wt %. In addition to the second monomer, the composition may further comprise additional polymerizable monomers, including combinations of two or more such monomers. A suitable photoinitiator is included within the composition to facilitate curing by UV radiation. Preferred are those initiators suitable in the formation of clear coatings having a low degree of observable color. Photoinitiator concentrations within the composition may vary depending on the nature of the other components of the composition and the nature of the photoinitiator. A typical concentration for the photoinitiator is between about 2 and 10% by weight.
Certain terms will be understood to have certain meanings, as set forth herein. xe2x80x9cUltraviolet radiationxe2x80x9d and xe2x80x9cUV radiationxe2x80x9d are used interchangeably to refer to the spectrum of light comprising wavelengths within the range from about 180 nm to 400 nm. xe2x80x9cCoatable compositionxe2x80x9d means a liquid composition that can be applied to a substrate and thereafter solidified (e.g., by UV curing) to form a hardened coating on the substrate. xe2x80x9cRadiation curablexe2x80x9d, in referring to the coatable compositions, means that the coatable composition will form a hardened coating upon exposure to radiation such as UV radiation or visible light (e.g., 180 to 800 nm). xe2x80x9cSubstratexe2x80x9d refers to any surface upon which the coatable compositions of the invention are applied and includes without limitation, vinyl floor tiles (including tiles previously coated with floor sealer or the like), ceramic tiles, wood, marble, and the like. As used herein, xe2x80x9cacrylatexe2x80x9d will be understood to include acrylate and methacrylate species. xe2x80x9cMonomerxe2x80x9d refers to any chemical species having at least one free radical polymerizable group (e.g., acrylate, methacrylate). xe2x80x9cTertiary amine alcoholxe2x80x9d is meant to indicate a tertiary amine that includes alcohol functionality.
In another aspect, the invention provides a floor finishing system, comprising the radiation curable coatable composition described above and a primer composition, the primer composition coatable over a substrate. In this aspect of the invention, the coatable composition is as previously described. The primer preferably comprises an acrylated latex with a solids content in water between about 2 and about 40% by weight. The latex is applied to the substrate and dried prior to the application of the coatable composition. The primer provides a layer over the substrate to which the coatable composition may bond. Moreover, the cured coatable composition is readily strippable from the substrate when the latex primer is present.
In still another aspect of the invention, a method for applying a protective coating to a substrate, comprising:
(A) applying a radiation curable coatable composition to a substrate, the composition comprising:
(i) a first monomer comprising (a) polyfunctional isocyanurate having at least three terminal reactive groups reacted with (b) hydroxyalkyl acrylate and (c) tertiary amine alcohol in a molar ratio of a:b:c of about 1:1-2.5:0.5-2, wherein b+c is at least 3 and no greater than the total number of terminal reactive groups of (a),
(ii) a second monomer, and
(iii) photoinitiator; and
(B) hardening the composition to form a protective coating over the substrate by exposing the coatable composition to ultraviolet radiation.
In this aspect of the invention, the first monomer, the second monomer and the photoinitiator are as previously described. Overall, the coatable composition is preferably comprises at least about 90% solids (e.g., less than about 10% solvent). Hardening of the composition in step (B) may be achieved in air at prevailing temperature and humidity (e.g., at ambient conditions). Although high intensity radiation achieves faster curing of the coatable composition and is generally preferred in performing the hardening step (B), the coatable compositions can also be cured with low intensity UV radiation. Hardening of the coatable compositions at low UV intensities can be accomplished fairly quickly (e.g., less than 30 seconds) using a low intensity radiation source that provides at least one band of wavelengths less than about 300 nm and a second band between about 300 and 400 nm. Preferably, such a low intensity radiation source emits a first band of wavelengths centered around 254 nm and a second band centered between 350 and 370 nm (e.g., around 365 nm) to cure the coating (typically about 0.03 mm thick) in less than about 30 seconds. A suitable low intensity radiation source is one that provides a radiation intensity between about 5 and 15 mW per square centimeter. Preferably, the exposure of the coating to the low intensity radiation is for a period of up to about 30 seconds.
The foregoing method may also comprise, prior to the foregoing applying step (A), applying a primer composition to the floor and drying the primer composition to form a primer coat over the substrate. As discussed above, the preferred primer composition is an acrylated latex, preferably having a solids content between about 2 and about 40% by weight.
In still another aspect, the invention provides a coating derived from the foregoing radiation curable coatable composition. In another aspect, the invention provides a substrate coated with the aforementioned coating.
In still another aspect, the invention broadly provides a method for applying a protective coating to a substrate, comprising:
(a) applying a coatable acrylated latex primer composition to the substrate;
(b) drying the primer composition to form an acrylated polymer primer coat over the substrate;
(c) applying a radiation curable coatable composition to the primer coat; and
(d) hardening the radiation curable coatable composition by exposing the composition to ultraviolet radiation to form a protective coating over the substrate.
The details of the invention will be more fully appreciated by those skilled in the art upon consideration of the remainder of the disclosure including the detailed description of the preferred embodiment and the appended claims.